1. Field of the Invention
The present invention relates to a sled motor mounting structure and a sliding feed mechanism provided with the sled motor mounting structure, and in particular relates to a sled motor mounting structure and a sliding feed mechanism provided with the sled motor mounting structure, for example, to be used in CD-ROM drives and CD-R (CD-Recordable) drives.
2. Description of the Prior Art
Disc drives, such as CD-ROM drives and CD-R drives or the like, use a sliding feed mechanism to move an optical pick-up and the like in the radial direction of a disc. This sliding feed mechanism is generally constructed from a slider (carriage) guided in a freely slidable manner on a guide load, a rack gear mounted on the slider, a reduction gear which meshes with the rack gear, and a reversible DC motor which includes a rotation shaft and a gear mounted to the rotation shaft to mesh with the reduction gear. In order to miniaturize the reduction mechanism and reduce noise, a motor (hereafter referred to as the "sled motor") which includes a rotation shaft and a lead screw (worm) mounted on the rotation shaft is generally used as the DC motor. In this arrangement, the slider on which the optical pick-up and the like are provided is moved forward and backward in the radial direction of a disc by driving the sled motor in the forward and reverse directions.
In this connection, in a motor which is used as the sled motor described above, the rotation shaft of the motor is provided with a small play in the axial direction to enable smooth rotation of the motor, and as a result the rotation shaft is capable of a small degree of movement in the axial direction of the rotation shaft. Consequently, when the rotation shaft of the motor is rotated in the advancing direction (screw tightening direction) of the lead screw, the rotation shaft moves in the tip direction within the range of the play, and this causes a collar and a thrust washer to come into contact with the bearing of the motor, whereby the rotation load of the motor is increased.
To prevent such increase in the rotation load of the motor, in such prior art sled motor mounting structures and sliding feed mechanisms provided with the sled motor mounting structure, the tip of the rotation shaft of the motor is biased by a spring or the like toward the base end so as to resist any movement of the rotation shaft of the motor toward the tip direction as the lead screw rotates.
However, if the rotation shaft of the motor is biased in this way by a spring or the like, a resistance exerted to the rotation shaft increases during rotation due to the biasing force added thereto, thus making it necessary for the motor to supply a large torque. Consequently, a relatively large size motor capable of delivering a large torque greater than the originally required torque must be used for the sled motor provided in the prior art sliding feed mechanism. Further, in a method like that described above in which the rotation shaft is biased by a spring, there is a slight difference in the biasing force exerted on the rotation shaft depending on the direction of rotation, and this will result in uneven rotation.
In particular, in a CD-R drive, because a highly accurate writing characteristic is required to carry out data recording, it is necessary to accurately position the objective lens of the optical pick-up at the center of the actuator when writing in data, but if the sliding feed mechanism does not move smoothly, the objective lens of the optical pick-up will move or swing, thereby degrading the writing characteristics.